This invention relates to a transmission system for a marine drive.
In a conventional marine drive, including an engine and a propulsion unit, the engine is directly and mechanically connected to the propeller through a gear box. As a result, the speed of the propeller is always directly proportional to the speed of the engine in a ratio established by the gears of the gear box.
The characteristics of the marine drive, including the gear ratio in the gear box and the size and pitch of the propeller, are usually selected to provide optimum performance to the boat at or near its wide open throttle condition. This is because the boat is generally rated at or near wide open throttle conditions. However, with such a selection of the marine drive characteristics, performance of the boat under conditions other than at or near wide open throttle generally suffers.
One particular operating condition adversely affected by the usual selection of marine drive characteristics is low-speed boat operation, such as for trolling or docking. Due to the aforementioned direct connection of the propeller to the engine, the minimum operational speed of the boat is limited by the minimum engine speed, generally attained at idling conditions. Such boat speed, in turn, is generally determined by the propeller selected. Because the propeller is generally selected to provide optimum performance at other than low speeds, this results in an undesirably high boat speed at engine idle conditions, causing difficulty in docking or other low boat speed maneuvering. Furthermore, under some conditions such low engine idle speeds are unreliable, and stalling of the engine may result.
Therefore, the object of the present invention is to provide a marine drive which provides low boat speeds and which allows reliable engine operation at such low boat speeds, and which retains optimum performance of the boat at operating conditions other than low speed, such as at higher engine speeds and at wide open throttle. Another object of the invention is to provide a marine drive which facilitates propulsion direction changes, such as between forward and reverse.
To this end, the marine drive of the present invention utilizes a fluid coupling device between the marine drive engine and gear box. The fluid coupling includes a rotatable fluid pump connected to the engine and rotatable in response to rotation of the engine crankshaft. A rotatable turbine is driven by the fluid pump, and is connected to an output shaft coupled to the propulsion unit. The fluid coupling further includes fluid direction controlling means between the fluid pump and the turbine, for controlling the direction of impingement of fluid on the turbine. Such control of the fluid impingement direction governs the speed and direction of rotation of the turbine in response to rotation of the pump. The control of speed of rotation of the turbine allows control of the speed of rotation of the output shaft, to control boat speed. The control of direction of rotation of the turbine dictates of rotation of the output shaft, to govern the direction of propulsion of the boat. In one embodiment, the fluid direction controlling means comprises a stationary ring of vanes disposed between the fluid pump and the turbine. The vanes can either be permanently fixed or clutched to ground. The vanes are movable in response to direct or indirect actuation by the operator of the boat, to control the direction of the fluid from the fluid pump. The vanes act to absorb a certain amount of power from the fluid pump, and transmit only a portion of the available power to the turbine through the fluid medium. In this manner, boat speed, which is governed by rotation of the output shaft, may be substantially lower than engine speed. The vanes also can act to govern direction of rotation of the turbine to control the direction of boat propulsion.
A portion of the power available from the fluid pump 11 will be transferred to the fluid medium in the form of heat. Thus, a heat exchanger is provided adjacent a fluid sump through which the fluid circulates. This cools the fluid prior to its circulation back into the fluid coupling, to dissipate the absorbed energy.
The fluid coupling of the invention incorporates built-in inefficiencies which are effective to provide low boat speeds at engine speeds well above idle, dependinhg on the direction of the vanes. However, under certain operating conditions, such as when high boat speed is desired, it is desirable to eliminate such built-in inefficiencies. To this end, a clutch is provided between the fluid pump and the turbine, to eliminate the effect of the fluid coupling. In this manner, the fluid pump and the turbine can be directly mechanically coupled to bypass the fluid coupling in response to certain operating variables. For example, the pump and the turbine can be clutched together in response to a certain predetermined engine speed. When the pump and the turbine are clutched together, it is desirable to drain the fluid from the housing of the fluid coupling to a fluid sump, so as to reduce turbulence of the fluid and waste of power. Alternatively, if the vanes are clutched to ground, such clutching can be released so as to allow the vanes to rotate with the pump and turbine. In this instance, draining of the fluid coupling housing is unnecessary.
A brake is provided on the output shaft of the fluid coupling. The brake acts responsively to certain predetermined low speeds of rotation of the output shaft. Thus, when the output shaft rotates at a certain predetermined low speed, the brake physically engages the output shaft to prevent its rotation. This eliminates any low speed rotation of the turbine which may be caused by a change in fluid direction from the vanes due to varying engine and pump speeds when a neutral condition is desired.